1. Field of the Invention
The present invention relates to integrated circuits, more particularly, but not exclusively, to integrated circuits realized in M0S (Metal Oxide Semiconductor) or BIMOS (BIpolar and Metal Oxide Semiconductor) technology.
2. Discussion of the Related Art
It may be necessary to limit the output current to avoid destruction of an integrated circuit amplifier in case of shorting at the amplifier output, or even in case a load having a too low impedance is connected at the output.
Such output current limiting means are not necessarily implemented by specific circuit components. Indeed, in M0S technology, for example, the output stage of the amplifier is typically formed by an AB-class amplifier having a threshold gain equal to 1. M0S transistor technology is such that the internal resistor of a transistor, even at the maximum conduction state, limits the current to a reasonable value (which depends on its geometry), even if the output is shorted. If the shorting current is still too high with respect to the value that can be withstood by the transistor, it would still be possible to insert a resistor between the supply terminal and the source of the transistor.
However, in some circuits, this type of limiter is no longer possible, such as in the case of amplifiers in which it is desired to have a very high output voltage range, that is, to have extreme values very close to supply voltage values. By way of example, if the supply voltages are respectively 0 and 10 volts, it is desired that the output voltage of the amplifier can come within 50 or 100 mV of these values with a 10-k.OMEGA. charge, or within 600 mV of these values with a 600-.OMEGA. charge.
The circuits of this type do not allow, a priori, to insert a limiting resistor in the source of the output transistors because such a resistor automatically decreases the output voltage range of the amplifier, proportionally to the resistor value. Additionally, such circuits theoretically require large-size output transistors, capable of conducting a high current; hence, such transistors will not be operable to automatically limit the current to a moderate value in case of shorting.
An object of the invention is to realize an amplifier including means for limiting the output current that can be provided by the amplifier.